Port Bun expect.extend cross-runner matcher matrix

Tracks the focused Bun parity tranche under #66.

Scope:

• activate the byte-identical js/bun/test/expect-extend.test.js fixture
• await asynchronous asymmetric matcher results in toEqual/toStrictEqual
• expose matcher-context equality with initialized cycle tracking
• add expect.anything() and MatcherContext.utils.RECEIVED_COLOR
• discover inherited and class-prototype matchers in expect.extend
• preserve invalid-result validation, numeric matcher keys, matcher overrides, and error propagation
• add a permanent exact-count regression and pass the complete home_test gate

Validated locally before publication:

• expect-extend.test.js: 28/28 passed, 0 failed/TODO/unsupported
• preload fixture: 1/1
• asymmetric-throw fixture: 1/1
• jest-extended fixture: 57 passed with its pre-existing 1 todo
• full ./pantry/.bin/zig build test -Dfilter=home_test --summary failures: pass

Completed in 7565e65da. The byte-identical cross-runner fixture now passes 28/28 with 0 failures, TODOs, or unsupported tests. Home now awaits async asymmetric matcher results, provides cycle-safe matcher-context equality, supports expect.anything(), inherited/class matchers, numeric matcher keys, and RECEIVED_COLOR. Adjacent preload and asymmetric-throw fixtures remain 1/1, and the complete home_test gate passes.